1. Field of the Invention
Flutter is a lateral deflection or deformation that occurs in a spinning body (in this case a saw blade). When saw blades are improperly serviced or mounted, this phenomenon is most easily evidenced by the blade producing a swath or path through the material being cut which is wider than the blade's kerf or tooth width.
A saw blade, when rotated is acted upon by centrifugal force. This force creates the tendency to make matter move away from the center of rotation. The matter, in this case, a blade, will continue to increase in diameter until all centrifugally produced force has been dissipated or until the blade's inherent (tensile) strength prevents further outward movement of the material being acted upon. Tensile strength can most easily be described as the amount of attraction or gripping power one molecule has towards its neighboring molecules within a given material. In cases where centrifugal force (energy) has not been totally dissipated through the blade's growth and tensile strength prevents additional expansion, an alternate route of dissipation will be taken. The next least resistant route to equilibrium is laterally and deflection or flutter occurs.
The key to preventing saw blade flutter at operational speeds is to manually elongate the circumference in a specified portion of the saw blade body to a length greater than the normal pi.times.diameter=circumference equation would yield. The location of this artificially elongated circumference will either increase or decrease the blade's ability to dissipate centrifugally produced energy in relationship to the speed at which tensile strength would prevent further growth. When this manual deformation or elongation is correctly performed, all centrifugally produced energy will, through stretching, be dissipated at or slightly below the saw blade's operational speed (rpm's). Because all energy would be dissipated at or near operational speeds, no alternate route to equilibrium would be required and the saw blade would operate without flutter. Industry jargon refers to this phenomenon as a blade growing into itself or "snap-out".
The afore-mentioned deformation or manual elongation is performed by a process known as "roll tensioning". A roll tensioning machine consists of two (2) crowned wheels which are configured to oppose each other. The saw blade's body is positioned between these wheels at a predetermined location and the wheels are then moved towards each other via: a manual or motorized screw jack to exert a specific pressure. The blade is then slowly rotated and the portion of the blade which passes between the wheels is compressed and thereby elongated.
Prior to performing the afore-mentioned roll tensioning, a determination must be made as to where it will be placed and how much pressure will be applied. If a blade reaches its point of equilibrium below the operational speed (rpm's) of the sawing machine on which it is to be used, the blade's periphery is too short and it has grown into itself prematurely. The introduction of additional rpm's will cause the blade to flutter due to its inability to stretch any further. This condition indicates the need for an elongating tension roll as near to the blade's periphery as possible.
If rpm's above that of the sawing machine's operational speed are required for the blade to reach a point of equilibrium its periphery is too long and it will never achieve equilibrium in its present condition. There are not enough rpm's available to make it happen. Since roll tensioners cannot shorten an overly elongated circumference, an interior (nearer the blade's bore) roll must be applied to reestablish the correct relative circumference between the blade's interior portion and exterior portion. Interior being towards the bore and exterior being towards the periphery. Outside forces such as fatigue, metallurgical make-up, etc. make it necessary to perform numerous evaluations and corrective actions during the life of a saw blade.
Tensile strength is best described as that property any material in question has to remain attracted to its self or its degree of molecular adhesion.
Current state of the art requires that an experienced hammersmith utilize judgment based on years of experience to determine to what degree a saw blade will expand when transitioned from the static to the dynamic state. The hammersmith utilizes what he knows about material strength, fatigue, etc. from his past experiences in a effort to determine the amount and location of roller tension induced deformation required to make the blade's point of equilibrium or snap out coincide with the operational speed of the sawing machine being used. Current art relies solely on judgment calls which generally vary from hammersmith to hammersmith. Since current art does not afford exacting measurements, it is truly an art form and not a scientific process.
Amounts of flutter and the speeds at which they occur vary widely from blade to blade due to some and possibly all of the following factors:
Variances in rpm's PA1 Variances in metallurgical make-up PA1 Variances in heat treating during production PA1 Variances in fatigue induced hardness PA1 Variances in tensioning PA1 Variances in amounts of operationally induced heat PA1 1) Lateral flutter to the right only at a given rpm (negative) PA1 2) Lateral flutter to the left only at a given rpm (positive) PA1 3) Total of all lateral flutter at a given rpm (negative & postive)
Some of the determination to be made by the hammersmith prior to preparing a blade for operation are as follows:
1) How much a blade's static circumference must be increased or its relative circumference decreased to produce a state of equilibrium at operational speeds.
2) To what degree a blade is fatigued and to what degree this will reduce its ability to expand when acted upon by centrifugal force
3) At what rotational speed is the blade currently reaching its point of equilibrium.
4) Can this blade be made to run harmoniously with a multitude of other blades on a common arbor in spite of their different operational characteristics?
The above noted variances and required determinations are not intended to be all-inclusive.